In-situ analysis of pectic polysaccharides in seed mucilage and at the root surface of Arabidopsis thaliana

Pectic polysaccharides are a complex set of macromolecules of the primary c ell wall matrix with distinct structural domains. The biosynthesis, organis ation and function of these domains within cell wall matrices are poorly un derstood. An immersion immunofluorescence labelling technique was developed for the in-situ analysis of pectic polysaccharides at the surface of seeds and seedlings of Arabidopsis thaliana (L.) Heynh., and used to investigate the occurrence of pectic homogalacturonan (HG) and rhamnogalacturonan-I (R G-I) epitopes. Seed mucilage appeared to consist of two regions: a highly m ethyl-esterified HG was a major component throughout the mucilage, while an inner region with relatively low porosity was stabilized by calcium-based HG cross-linking. The small size and transparency of Arabidopsis roots allo wed the occurrence of pectic HG and RG-I epitopes at root surfaces to be di rectly determined on whole-mount preparations. Pectic epitopes were not dis tributed evenly over root surfaces and were notably absent from lateral roo t apices and from the surface of root hairs. The use of defined antibody pr obes in the immersion immunolabelling protocol will be useful for the analy sis of the influence of growth conditions and genetic factors on pectic pol ysaccharides in Arabidopsis.